Far-field component of the benthic plume that consists mainly of fines; sedimentary particles which drift with the bottom current and slowly settle to the sea floor, generally outside the specific area of activity. Compare to benthic plume and surface plume.

Rare Earth Element

A relatively abundant group of 17 chemical elements, including the lanthanides and the actinides. Originally called 'rare' as they were unknown in their elemental form and difficult to extract from the rocks that contained them. Rarely concentrated in high enough quantities to be mined economically. Abbreviated to REE.

Redox system

One essential chemical reaction is oxidation (giving electron) and reduction (removing electron). The chemical tendency (environmental strength) of oxidation can be expressed by redox potential (mv) that can be measured by an Eh/Ph meter. Eh is strongly correlated to the dissolved oxygen concentration in the sediment.

Reduced

A substance that has undergone reduction. Opposite of oxidized.

Reduction

Chemical transformation of a substance by the gain of hydrogen or electrons. Opposite of oxidation.

REE

Rare Earth Element(s).

Remotely Operated Vehicle

Unmanned, research submersible that is controlled remotely usually from a support vessel or platform. Abbreviated to ROV. Examples include Jason (USA), Jason Junior (USA), Kaiko (Japan), Robin (France), Tiburon (USA) and Victor-6000 (France). Compare to Autonomous Underwater Vehicles and Deep-Sea Research Vehicles.

Research Submersible

Underwater vehicle used for sampling. The main benefits of research submersibles are the ability to control exactly where samples are taken and they allow for manipulative experiments. Collective term for Autonomous Underwater Vehicles, Remotely Operated Vehicles and Deep-Sea Research Vehicles.